The present invention relates to the field of pneumatically transporting suspended articles, and more particularly lightweight articles such as empty bottles or flasks made of plastics material, preforms, etc., for example.
To transport lightweight articles, and in particular plastics or similar bottles, it is known to use air conveyors that are fitted with blow means enabling a plurality of air jets to be created that are directed on the articles in their transport direction.
For articles that can be suspended, for example plastics bottles having a collar on the neck, it is more particularly the practice to use air conveyors which are fitted with a guide rail, more commonly referred to as the under-collar guide, along which the articles are guided and transported while being suspended from the collar or the like. That type of conveyor is described, for example, in U.S. Pat. No. 4,284,370 or indeed in U.S. Pat. No. 5,161,919. It implements a main air trunk, commonly referred to as a xe2x80x9cplenumxe2x80x9d, extending along the path of the articles, and a blow channel communicating with the main air trunk via blow slots or the like. The main trunk is fed with air, e.g. by means of a plurality of blowers suitably distributed along its length; this air is delivered via the blow slots in the form of a plurality of air jets that serve to propel the articles along the blow channel. In U.S. Pat. No. 4,284,370, the blow channel is rectangular in section and the blow slots are disposed above the guide rail, thereby making it possible to propel the articles by blowing on them above their collars. In U.S. Pat. No. 5,161,919, the blow channel is in the form of an upside-down V-shape, and the blow slots are disposed beneath the guide rail, thereby enabling articles to be propelled by blowing on them beneath their collars.
While they are being transported, articles suspended from their collars, for example, can swing sideways relative to the longitudinal direction of the conveyor, particularly in curved portions (bends) of the conveyor. To limit this sideways displacement of the articles, it is presently commonplace to fit air conveyors with lateral guides disposed on either side of the path of the articles, with the spacing between the lateral guides determining the maximum angle through which the articles can swing sideways. While they are being transported, bottles also tend to oscillate longitudinally with alternating forward and backward motion relative to the vertical, and that can hamper conveyance, and can also give rise to a risk of articles becoming jammed, e.g. by becoming jammed in a forward or backward position. To mitigate the front/back oscillations of the articles, proposals have already been made in U.S. Pat. No. 5,421,678 to fit an air conveyor with at least one longitudinal brush which extends along the path of the articles and which serves to apply a braking force continuously on the articles that are being transported so that the articles are transported in a stable manner, being tilted rearwards from the vertical relative to the transport direction by some given angle, referred to below as the xe2x80x9cconveyingxe2x80x9d angle. More particularly, in the embodiment shown in FIG. 4 of that publication, the conveyor is fitted with two top and bottom pairs of lateral guides referenced 42 and 44 to limit sideways motion of the articles, and it is fitted with a brush referenced 60 that is fixed to one of the two bottom lateral guides 44. A first drawback of that solution is that the conveying angle depends in particular on the speed of the conveyor and on the material from which the bottles are made; in addition, it is not possible to guarantee a minimum conveying angle. A second drawback is that, in use, it is observed that the bristles of the brush become worn, and above all that the bristles take up a preferred orientation because of their repeated contact with the articles, thereby causing the article conveying angle to change over time. In order to conserve the proper conveying angle, it is therefore necessary on a regular basis to adjust the distance between the bristles of the brushes and the bodies of the articles, and in the end to replace brushes that have worn out.
A main object of the present invention is to propose a novel solution that also serves to improve the conveyability of suspended articles transported in air conveyor, by mitigating the problems of front/back oscillation and of lateral motion of the suspended articles while they are being transported, but which does not present the above-mentioned drawbacks of the solution recommended in U.S. Pat. No. 5,421,678.
This object is achieved by the invention which provides an air conveyor for transporting suspended articles under the drive of air jets, the conveyor being characterized in that it comprises a bottom longitudinal guide that extends along the path of the articles, which guide comprises two facing longitudinal guide walls and is positioned or suitable for being positioned relative to the suspension points of the articles in such a manner that an article suspended on the conveyor comes into contact via its base with the inside faces of the two guide walls which hold it tilted relative to the vertical and in a rearward direction relative to the transport direction at a minimum conveying angle.
In the invention, the bottom longitudinal guide performs two functions: it limits sideways motion of the articles and it imposes a minimum conveying angle, thereby making it possible to prevent front/back oscillation of the articles while they are being transported.
In a preferred embodiment, the conveyor is provided with means for adjusting the distance between the bottom longitudinal guide and the article support point in a vertical direction. This provides a modular air conveyor which can be adapted simply and quickly to the format of articles that are to be transported (i.e. their shape and size).
In a particular embodiment of the invention, the means for forming the transport air jets for propelling the articles along the conveyor are designed in such a manner as to generate at least lower air jets which are directed against the articles beneath their suspension points. Prior to the invention, implementing bottom transport air jets acting on a portion of the articles situated beneath the suspension point thereof, constituted a major source of instability for the transported articles, in particular when the transported articles were suspended from a carrier zone situated well above their centers of gravity, as is the case, for example, of plastic bottles that are transported by being suspended from projections on their necks. In that type of conveyor, it was therefore necessary in the past for the purpose of limiting the risk of article instability, and even though it could not be eliminated, to restrict the power of the bottom transport air jet and/or to position said bottom transport jets as close as possible to the article suspension point, with this being to the detriment of conveyor speed. Implementing a bottom longitudinal guide of the invention advantageously makes it possible to mitigate that drawback since the guide makes it possible to transport articles in a rearwardly-sloping position, thus avoiding any forward tilting of the articles under drive from the bottom transport air jets. This makes it possible to increase the power of the bottom transport air jets and/or to apply said bottom transport air jets to any of the portions of the articles situated beneath their suspension points, without interfering with the stability of the articles while being conveyed.